Patent GB-1523611-A (GB)
Title: Stereoscopic film viewers
IPC: G02B27/22
Filed: 1975-09-08
Abstract: 1523611 Stereoscopic viewers G CECCHINI 8 Sept 1975 [20 Sept 1974] 36854/75 Heading G2J A stereoscopic film viewer comprises means for driving the film past a viewing station, and a locating finger, spring-loaded towards the film, of such a profile that it engages and locks into a locating hole corresponding to each pair of film frames. A reciprocable drive member is formed by two sliders 70, 72, one of which moves within the other, and which are urged to the right (position of Fig. 10) by a spring 88. Slider 70 has a resilient portion 102 which has a cam 104 on its under side (seen more clearly in Fig. 23 not shown). Slider 72 has a rack portion 80, which can engage with a gear 62 to actuate the film transport, gear 62 engaging with a gear 36A secured to the drive member 36, Fig. 5 (not shown) which winds on the film take-up reel. The film is a 35 mm strip having sprocket holes along both edges, which has been cut longitudinally along its centre, to form two equal half-strips 11, one of which is shown in Fig. 4. A half-strip is used in the viewer of the invention, consecutive frames 14A 14B forming the stereoscopic pair of pictures viewed. One large hole 16 is made by joining together two consecutive sprocket holes 1A, so that there is one large hole corresponding to each stereo pair of pictures, the hole being used to position the film accurately in the viewer. The locating finger 18 is carried by a body 94 which is entrained between wall portions 92, the body being urged by a spring 96 so that finger 18 abuts against the film. When the film is positioned so that a hole 16 is aligned with the finger, this enters into the hole, as seen in Fig. 19. The shape of the finger is such that it holds and locks the film against further movement. A pin 98 rigid with body 94 projects towards cam 104, but is out of contact therewith in a viewing position (Fig. 19). To view the next pair of frames, the slider 70 is pushed to the left by means of the button 90 at one end (Figs. 10, 20, 22). Slider 70 has a limited degree of movement, because of recessed portions 84, before the shoulders of the recessed portions engage stops 76A on slider 72. During this period, while the play between the two sliders is being taken up, a ramp portion 106 of cam 104 engages pin 98 and displaces it so that body 94 is displaced downwards (Fig. 19), and hence finger 18 is retracted out of engagement with hole 16. The film is thus free to move to the right. After the play has been taken up, the two sliders then move together, against a spring 88. The rack portion 80 of slider 72 engages and drives the train of gears which wind on the film. The pin 98 is now released from cam 104, and finger 18 is biased by spring 96 back into contact with the film. This has now moved on, however, so that hole 16 is no longer in alignment with finger 18, which slides over the normal-sized perforations 1A until another hole 16 is reached. This is now entered again by finger 18, which thus halts the film feed, and locks it against further movement to the left. The film is now positioned for viewing the next pair of stereo pictures. On releasing button 90, spring 88 drives slider 70, and consequently slider 72 also, to their initial positions. During this return movement the film drive is not affected because the drive mechanism includes a coupling which engages in one rotational direction only.